Two emerging trends in treatment explain a steady increase in IVF success rates


A large cohort study of Sweden’s national IVF registry, which included nearly 125,000 treatments performed between 2007 and 2017, concluded that the steady increase in the birth rate can be attributed to two emerging IVF clinical trends. : the transfer of embryos to the blastocyst phase of their development and the increasing use of embryo freezing (with the rapid freezing technology of vitrification).

The results of the study, which now quantify the impact of these two widely adopted techniques, are presented in a poster at this year’s annual ESHRE online meeting by Dr. Zoha Saket of Sahlgrenska University Hospital in Gothenburg, Sweden. He describes the technique of blastocyst transfer in IVF (with embryos cultured for five or six days), and especially when transferred after freezing, as an important contributor to the improvement of the live birth rate over time. “.

National data analyzed for the study showed that cumulative live birth rates increased over the decade, from 27% in 2007 to 36% in 2017 for each egg collection cycle. These “cumulative” indices, now accepted, represent the most revealing indicator of IVF success, indicating a real-life outcome of a fresh treatment cycle plus any subsequent cycle of additional frozen blastocysts. The increase in the cumulative live birth rate was found to be independent of maternal age, number of eggs recovered, and number of previous live births of IVF, suggesting that their explanation lies in the self. treatment and not in other predictive factors.

Single blastocyst transfer emerged as a growing strategy in Sweden during the study period, and no less important – as was followed worldwide – to reduce the risk of multiple pregnancies. In addition, Dr. Saket said, even when a new embryo transfer was performed on day two or three (in the traditional stage of cleavage), the culture of all additional embryos in the blastocyst phase. would select ”embryos with more possibilities of implantation and thus increase the possibility of a live birth within it [initial] oocyte aspiration cycle “.

In fact, blastocyst transfer has been associated with most studies with higher birth rates than cleaved embryos. One explanation is that blastocyst transfers have been considered more physiological (as in natural pregnancies) and therefore provide an additional means of embryo selection.

Dr Saket said the rate of blastocyst transfers increased rapidly in Sweden during the study period, for new transfers from 5% in 2007 to 31% in 2017 and for frozen-thawed transfers from 6% in 88%. Embryo transfer in the cleavage phase decreased accordingly, while the increase in blastocyst transfer rate followed the trend of increasing live . Similarly, the introduction of rapid freezing by vitrification a decade ago allowed for a higher embryo survival rate than with slower freezing techniques.

Although it was an observational study looking back over time, Dr. Saket said adjustments were made for the most important factors that could influence outcomes and that these factors did not affect improvement. gradual accumulation of the birth rate. In addition, the increasing use of the transfer of a single embryo over time would indicate that this improvement in outcome was not explained by the number of embryos transferred.

“We have seen a substantial increase in the live birth rate over time,” Dr. Saket said, “and this has gone hand in hand with an increase in blastocyst transfer, especially when used with frozen treatments.This development, when observed in parallel with a high and increasing use of single blastocyst transfer, also translates into a low multiple birth rate.

“In addition, as techniques for embryo culture to the blastocyst stage and for cryopreservation have improved, more blastocysts are available for transfer. And this has important implications for patients: that a smaller number of egg collection treatments may be needed to obtain a live one and that time can be shortened to achieve this. A high single blastocyst transfer rate will also reduce the risk of multiple pregnancies. “

Blastocyst transfer in IVF

  • An embryo cultured for five to six days after ovarian recovery is known as a blastocyst. Transfer of a blastocyst to IVF is said to be more physiological both in the pregnancy that is implanted in the uterus, and in a natural pregnancy, in the blastocyst phase. Currently, most national IVF records show that about 75% of all embryo transfers occur in the blastocyst phase.
  • Overall, studies show that treatment cycles with blastocyst transfers have slightly higher success rates than those with cleavage phase transfers (day 3). Development in the laboratory up to the blastocyst stage provides the embryologist with an additional means of selection for transfer.


  • Vitrification, a fast-freezing technology that reduces cells to a glass-like state in seconds, has revolutionized freezing in recent years. The speed of the technology prevents ice crystals from forming, which on thawing could have damaged frozen cells. This is why eggs — and not just embryos — can now be frozen without damage and without loss of viability.
  • This is also the reason why it was vitrified they have high survival rates after thawing. Vitrification of an embryo (or blastocyst) also means that the transfer of a frozen-thawed embryo should not be done in the same “fresh” cycle in which the ovaries were stimulated with fertility hormones, which some studies they have been shown to be detrimental to implantation and the uterine environment. The huge clinical benefit of freezing means that one embryo can be transferred at a time, thus avoiding the risk of multiple pregnancies, a policy enthusiastically followed in Sweden.

A large cohort study confirms a small added obstetric risk arising from the transfer of more developed embryos

More information:
Poster 0767: Cumulative birth rate after IVF: trend over time and the impact of blastocyst culture and vitrification

Citation: Two emerging trends in treatment explain a steady increase in IVF success rates (2021, June 30) recovered on June 30, 2021 at -trends-treatment-steady-ivf.html

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